Netty

1.概述

Netty对NIO的API进行了良好的封装，完全可以将业务代码从网络IO中解放出来，具有高性能、 高吞吐量，低延迟等优点。经常被作为通信组件来使用,eg:Dubbo、RocketMq、Zookeeper等。

2.入门

        1）依赖

        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.35.Final</version>
        </dependency>

        2）服务端：

package org.example.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

import java.nio.charset.StandardCharsets;

public class NettyServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("NettyServerHandler ctx:" + ctx);
        System.out.println("NettyServerHandler 收到消息:" + buf.toString(StandardCharsets.UTF_8));
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ByteBuf buf = Unpooled.copiedBuffer("Netty ...".getBytes(StandardCharsets.UTF_8));
        ctx.writeAndFlush(buf);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("ctx:" + ctx);
        System.out.println("cause:" + cause);
        ctx.close();
    }
}

package org.example.netty;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class NettyServer {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
        NioEventLoopGroup workGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            socketChannel.pipeline().addLast(new NettyServerHandler());
                        }
                    });
            System.out.println("netty server start.....");

            ChannelFuture sync = serverBootstrap.bind(35599).sync();
            System.out.println(".....");

            sync.addListener(channelFuture -> {
                if (channelFuture.isSuccess()) {
                    System.out.println("监听端口35599成功");
                } else {
                    System.out.println("监听端口35599失败");
                }
            });

            sync.channel().closeFuture().sync();
            System.out.println("通道关闭");

        } finally {
            bossGroup.shutdownGracefully();
            workGroup.shutdownGracefully();
            System.out.println("线程池关闭");
        }
    }
}

         3）客户端：

package org.example.netty;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

public class NettyClient {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup nioEventLoopGroup=new NioEventLoopGroup();

        try {
            Bootstrap bootstrap=new Bootstrap();
            bootstrap.group(nioEventLoopGroup)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            socketChannel.pipeline().addLast(new NettyClientHandler());
                        }
                    });
            System.out.println("netty Client start.....");

            ChannelFuture sync = bootstrap.connect("127.0.0.1", 35599).sync();

            System.out.println("netty Client connect.....");

            sync.channel().closeFuture().sync();
        }finally {
            nioEventLoopGroup.shutdownGracefully();
        }
    }
}

package org.example.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.concurrent.EventExecutorGroup;

import java.nio.charset.StandardCharsets;

public class NettyClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("客户端激活:  " + ctx);
        String msg = "Netty Client ...";
        ByteBuf buf = Unpooled.copiedBuffer(msg.getBytes(StandardCharsets.UTF_8));
        ctx.writeAndFlush(buf);
        System.out.println("客户端发送消息:" + msg);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        System.out.println("ctx:" + ctx);
        System.out.println("客户端收到消息:" + buf.toString(StandardCharsets.UTF_8));
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("ctx:" + ctx);
        System.out.println("cause:" + cause);
        ctx.close();
    }
}

3.线程模型

4.高性能

•         NIO多路复用非阻塞        
•         零拷贝（使用直接内存，减少了堆内、堆外的拷贝）
•         主从Reactor线程模型提升并发量
•         单线程串行执行（减少竞争）